1. Field of the Invention
The present invention relates to a display panel including pixels each provided with a light emitting element.
2. Description of Related Art
An organic electroluminescence element has a laminated structure, for example, of an anode, an organic compound layer and a cathode stacked on a substrate. When a voltage is applied between the anode and the cathode, positive holes and electrons are injected into the organic compound layer to generate an electric field, thereby to emit light.
In a display panel of an active matrix driving type, a plurality of thin film transistors are provided for each pixel or dot, which allow the organic electroluminescence element to emit light. For example, in the display panel disclosed in JP-H8-330600A, two thin film transistors are provided for each pixel. A plurality of organic electroluminescence elements are formed and disposed in a matrix arrangement by a patterning process, and also in the patterning process, anodes are formed independently from each other in a bottom layer side which is connected to the thin film transistors. Meanwhile, the cathode is formed as a single film of a counter electrode to all pixels.
In order to drive the display panel, there are provided a plurality of scanning lines and signal lines on the display panel. When the display panel is driven, a signal is sequentially sent to the scanning lines to sequentially select the scanning lines, and signals corresponding to gradients are output while the scanning lines are selected, whereby a gradient signal is written on the pixel locating at the cross point of the selected scanning line and the signal line.
With respect to the driving system of the display panel, there are two systems: one is a voltage designating system for performing control according to a voltage value of a gradient signal to be output to the signal lines, and the other is a current designating system performing control according to a current value of a gradient signal to be output to the signal lines. In the voltage designating system, since the signal to be applied to the signal lines is a voltage, a signal reaches a predetermined potential in a certain time when a parasitic capacitance exists in the signal lines in some measure. Such a delay due to a parasitic capacitance exerts a large influence to a display of the current designating system, in particular. That is, in the current designating system, since the light emitting element itself can emit light with a weak current, a weak current flowing through the signal lines is enough, however, when the parasitic capacitance associated with lines is large, the current takes a time to reach a predetermined current value.